• 한국표면공학회지
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• 제20권3호
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• pp.106-117
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• 1987

The microhardness and the structural characteristics of the chemically vapor deposited TiN film on the 430 stainless steel substrate have been investigated with various deposition parameters such as the deposition time, the total flow rate, the flow rate ratio $(H_2/N_2)$, and the deposition temperature. The most important factor to affect the microhardness of the TiN film in this study was the denseness of the structure in connection with the degree of the lattice strain. The relationship between the lattice parameter changes and the grain size variation under all deposition conditions generally followed the grain boundary relaxation model. The (111) preferred orientation prevailed in the early stage of the deposition conditions, however, the (200) preferred orientation was developed in the later stage. The surface morphology at optimum conditions displayed a dense diamond shaped structure and the microhardness of the films was high (1700-2400Hv) regardless of the type of the substrates used.

• 한국콘텐츠학회논문지
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• 제13권12호
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• pp.893-899
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• 2013

본 연구에서는 0.243% 불화나트륨 함유된 어린이 불소치약을 적용하여 유치의 재광화 효과를 알아보기 위하여 유치의 법랑질 표면경도 측정과 치아의 무기질 성분인 Ca, P의 성분분석을 시행하여 분석한 결과, 0.243% 불화나트륨이 함유된 어린이 불소치약의 사용은 유치의 법랑질의 경도를 증가시켜 치질의 강도를 높이고, 치아의 주요성분인 Ca, P의 수치가 증가 됨을 확인하였다. 따라서 영유아 구강건강 관리를 위하여 불화나트륨이 함유된 어린이 불소치약으로 칫솔질을 하게 되면 유치의 효과적인 재광화가 이루지는 것으로 사료되며, 유치의 표면의 미세경도와 무기질 성분분석을 통하여 치질의 재광화 촉진에 영향을 미치는 것으로 판단된다.

• 한국치위생학회지
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• 제1권1호
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• pp.125-132
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• 2001

This study was carried out to investigate the effect of multi or single application of fluoride plus 0.05% NaF solution on the remineralization of dental caries lesion. The microhardness changes of enamel surface were measured after application of fluoride and precipitation of 0.05% NaF solution on 6 groups of cow's tooth on which the artificial carious lesions were formed first. Test groups were calssified into two step application with NaF, $SnF_2$ and APF under different application time conditions plus 0.05% NaF solution(group I, II, III, IV) and single application with APF plus 0.05% NaF solution (group V) and control(0.05% NaF solution only, group IV). The obtained results were as follows. 1. Regarding microhardness change of enamel surface. microhardness increments in group I(NaF for 1 minute+APF for 3 minutes+0.05% NaF solution for 1 minute), II($SnF_2$ 1 min+APF 3 min+NaF sol.), III($SnF_2$ 2 min+APF 2 min+NaF sol.), IV(NaF 2 min+APF 2 min+NaF sol.) and V(APF 4 min+NaF sol.) were significantly greater than group VI.(P<0.05) 2. Microhardness changes of shorter application time of $SnF_2$ (group II) were significantly greater than group III. (P<0.05) 3. Microhardness changes were variable with kinds of fluoride, application sequence and application time of fluoride. but had no relation with the number of fluoride application.

• 대한소아치과학회지
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• 제25권4호
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• pp.731-748
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• 1998

The purpose of this study was to test the hypothesis that the more thorough cure of lightactivated composite resin could be obtained if a new way of delivering the light source deep through the resin body is developed when compared to the conventional bulk cure or incremental cure. Using cylindrical resin blocks and natural teeth, various curing conditions were tested for their effects on the degree of microleakage and microhardness. Data were analyzed statistically using One-Way ANOVA and Scheff's Multiple Range test. The results of the present study were as follows: 1. The increment of reduction in microhardness with depth was shown to be higher in group I and II than in group II and V. 2. At the level of lower inner surface and the bottom surface, significantly lower microhardness values were obtained in group I and II when compared to group III, IV and V. Group IV showed the lowest value among three groups(III, IV, V) representing the only statistically significant difference from group V(p<05). 3. Differences between groups in the degree of microleakage detected were shown to be statistically significant (p<05) with the exception of group IV and V at both occlusal and gingival margins. 4. Based upon the above-mentioned results, commonly cited recommendation of incremental curing is strongly supported and the light-transmitting wedge insertion method can be considered as a effective and feasible clinical procedure for the better curing of composite resin. However, more studies under a variety of conditions should be completed before this method is applied actually to the clinical setting.

• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4072-4083
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• 2022

Ultrasonic impact treatment (UIT) is carried out on the Ni-based alloy stainless steel pipe gas tungsten arc welding (GTAW) girth weld, the differences of microstructure, microhardness and shear strength distribution of the joint before and after ultrasonic shock are studied by microhardness test and shear punch test. The results show that after UIT, the plastic deformation layer is formed on the outside surface of the Ni-based alloy overlayer, single-phase austenite and γ type precipitates are formed in the overlayer, and a large number of columnar crystals are formed on the bottom side of the overlayer. The average microhardness of the overlayer increased from 221 H V to 254 H V by 14.9%, the shear strength increased from 696 MPa to 882 MPa with an increase of 26.7% and the transverse average residual stress decreased from 102.71 MPa (tensile stress) to -18.33 MPa (compressive stress), the longitudinal average residual stress decreased from 114.87 MPa (tensile stress) to -84.64 MPa (compressive stress). The fracture surface has been appeared obvious shear lip marks and a few dimples. The element migrates at the fusion boundary between the Ni-based alloy overlayer and the austenitic stainless steel joint, which is leaded to form a local martensite zone and appear hot cracks. The welded joint is cooled by FA solidification mode, which is forming a large number of late and skeleton ferrite phase with an average microhardness of 190 H V and no obvious change in shear strength. The base metal is all austenitic phase with an average microhardness of 206 H V and shear strength of 696 MPa.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2013년도 춘계학술대회 논문집
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• pp.109-110
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• 2013

Medium carbon steel was aluminized by hot dipping into molten Al or Al-1%Si baths. After hot-dipping in these baths, a thin Al-rich topcoat and a thick alloy layer rich in $Al_5Fe_2$ formed on the surface. A small a mount of FeAl and $Al_3Fe$ was incorporated in the alloy layer. Silicon from the Al-1%Si bath was uniformly distributed throughout the entire coating. The hot dipping increased the microhardness of the steel by about 8 times. Heating at $700-1000^{\circ}C$ however decreased the microhardness through interdiffusion between the coating and the substrate. The oxidation at $700-1000^{\circ}C$ in air formed a thin protective ${\alpha}-Al_2O_3$ layer, which provided good oxidation resistance. Silicon was oxidized to amorphous silica, exhibiting a glassy oxide surface.

• Restorative Dentistry and Endodontics
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• 제44권4호
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• pp.41.1-41.13
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• 2019

Objectives: This paper presents a systematic review and meta-analysis of the effect of preheating on the hardness of nanofilled, nanoceramic, nanohybrid, and microhybrid resin composites. Materials and Methods: An electronic search of papers on MEDLINE/PubMed, ScienceDirect, and EBSCOhost was performed. Only in vitro studies were included. Non-English studies, case reports, clinical trials, and review articles were excluded. A meta-analysis of the reviewed studies was conducted to quantify differences in the microhardness of the Z250 microhybrid resin composite using the Comprehensive Meta-Analysis software. Results: Only 13 studies met the inclusion criteria for this systematic review. The meta-analysis showed that there were significant differences between the non-preheated and preheated modes for both the top and bottom surfaces of the specimens (p < 0.05). The microhardness of the Z250 resin composite on the top surface in the preheated mode (78.1 ± 2.9) was higher than in the non-preheated mode (67.4 ± 4.0; p < 0.001). Moreover, the microhardness of the Z250 resin composite on the bottom surface in the preheated mode (71.8 ± 3.8) was higher than in the non-preheated mode (57.5 ± 5.7, p < 0.001). Conclusions: Although the results reported in the reviewed studies showed great variability, sufficient scientific evidence was found to support the hypothesis that preheating can improve the hardness of resin composites.

• 대한치위생과학회지
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• 제5권1호
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• pp.29-38
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• 2022

Background: This study aimed to compare the remineralization effects of sodium caseinate and other substances on artificially demineralized enamel. Methods: We selected 25 healthy human premolars and molars and produced a total of 75 specimens by dividing them into five groups: control group, with distilled water; experimental group 1 (EG1), with 3% sodium caseinate; EG2, with 10% sodium caseinate; EG3, with casein phosphopeptide-amorphous calcium phosphate (CPP-ACP); and EG4, with 0.05% NaF. Subsequently, the specimens were immersed in an artificial demineralization solution for 60 min. The demineralized specimens were then immersed in a remineralization solution for 7 days. Surface microhardness was measured using a microhardness tester, and remineralized lesions were observed under a scanning electron microscope (SEM). Regarding statistical analysis, the paired t-test and analysis of variance were performed using the SPSS program. Results: Although the surface hardness of the remineralized lesions increased significantly in all groups (p<0.05), the average increment did not differ significantly between the groups. The surface microhardness of CPP-ACP was the highest, followed by that of 0.05% NaF and 10% sodium caseinate. The remineralization effect of sodium caseinate was similar to that of 0.05% NaF. SEM confirmed that all groups treated with the remineralization solution were remineralized. Conclusions: Although the remineralization effect of sodium caseinate was slightly lower than that of CPP-ACP, it was similar to that of 0.05% NaF. Therefore, to enhance the remineralization effect of sodium caseinate, the appropriate concentration and application time should be determined.

• 한국치위생학회지
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• 제13권2호
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• pp.351-360
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• 2013

Objectives : The purpose of this study was to evaluate the effects of tooth bleaching agent contained 15% carbamide peroxide on the color, microhardness and surface roughness of tooth-colored restorative materials by using pH cycling model. Methods : Four types of tooth-colored restorative materials, including a composite resin(Filtek Z350 ; Z350), a flowable composite resin(Filtek P60 : P60), a compomer(Dyract$^{(R)}$ AP ; DY), and a glass-ionomer cement(KetacTM Molar Easymix ; KM). were used in the study. Eighty-eight specimens of each material were fabricated, randomly divided into two groups(n=44): experimental group(15% carbamide peroxide) and control group(distilled water). These groups were then divided into four subgroups(n=11). All groups were bleached 4 hours per day for 14 days using pH cycling model. The authors measured the color, microhardness, and roughness of the specimens before and after bleaching. The data were analyzed with ANOVA and T-test. Results : Z350 and P60 showed a slight color change(${\Delta}E^*$), whereas DY and KM showed significantly color change(p<0.05). Among them, the greatest color change was observed in DY. Percentage microhardness loss(PML) of the distilled water group was 1.8 to 5.1%, and 15% peroxide peroxide group was 5.0 to 25.2%. Microhardness of DY and KM showed a statistically significant decrease(p<0.05). Roughness was increased in all groups after bleaching. Z350 and P60 does not have a significant difference(p>0.05), however DY and KM significantly increased more than the 0.2 ${\mu}m$(p<0.05). Conclusions : The effects of bleaching on restorative materials were material dependent. It is necessary to consider the type of the material before starting the treatment.

• 한국치위생학회지
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• 제8권4호
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• pp.11-18
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• 2008

The purposes of this study were to examine the effect of 35% Carbamide Peroxide(CP) bleaching agent on the changes in physical and chemical characteristics of tooth. The effect of bleaching agent on enamel was analyzed using Hardness test, SEM and EDS. The microhardness between bleached groups after bleaching showed statistically significant difference according to the paired t-test. The bleached enamel surface showed apparent morphological changes compared to the enamel, which was stored in distilled water only. The difference of the total mineral contents for the distilled water and Carbamide Peroxide did not show statistical significance. These results demonstrated that bleaching using 35% Carbamide Peroxide were adversely affects application time of experimental group and may the safety of using these agents for a short time in dentist-monitored bleaching.